Infant Immunizations Not Shown to Be Harmful to Children's Immune Systems

WASHINGTON -- The current immunization schedule calling for infants to get up to 20 vaccinations by the age of two does not increase the risk of contracting Type 1 diabetes or various infections, such as pneumonia and meningitis, says a new report from the National Academies' Institute of Medicine. The evidence is inconclusive as to whether the immunization schedule increases the risk of asthma. The committee that wrote the report said there is no need for a federal review of the schedule for infant immunizations at this time.

The increase in vaccine number and doses given to infants in recent years has led to concerns among some parents about possible adverse effects from immunizing infants so heavily. One concern is related to the higher incidence of diseases associated with immune system dysfunction, such as asthma and Type 1 diabetes -- an insulin-dependent form of the disease, previously referred to as juvenile diabetes. Although genetic factors are known to affect the risk of developing these diseases, the increase in their incidence seems more likely to be the result of environmental factors. Immunization has been proposed as one possible adverse environmental modifier of immune function.

"Like any drug, no vaccine is 100 percent safe, but this report should at least assure parents that getting so many immunizations during infancy is not causing diabetes or increasing the risk of certain serious infections," said committee chair Marie McCormick, professor and chair, department of maternal and child health, Harvard School of Public Health, Boston.

The immunization schedule in this country has grown complex over the last20years. In 1980, infants were vaccinated against four diseases -- diphtheria, tetanus, pertussis, and polio. Today, most healthy infants get up to 15 shots of five vaccines by the time they are six months old, and up to 5 additional shots of seven more vaccines by age two. These immunizations protect against 11 diseases in total -- diphtheria, tetanus, pertussis, polio, measles, mumps, rubella, hepatitis B, Haemophilus influenzae type b (commonly referred to as Hib disease), varicella, and pneumococcus.

Despite the rise in the number of both vaccines and vaccine doses, exposure to vaccine antigens -- those portions of a foreign substance that trigger an immune response -- is lower than it used to be. This reduced antigen load is explained, in part, by the removal of two vaccines from the immunization schedule. Smallpox vaccine, which was discontinued in 1971, contained approximately 200 potentially antigenic substances. In addition, a new, streamlined form of pertussis vaccine, approved for use in 1991, reduced the number of potential antigens from approximately 3,000 to between two and five. Furthermore, vaccines added to the immunization schedule during the past two decades have relatively few antigens. The new hepatitis B vaccine, for example, contains only one antigen.

The committee reviewed eight studies of the relationship between multiple vaccinations and Type 1 diabetes, the autoimmune form of the disease in which the body produces antibodies against its own insulin-secreting pancreatic islet cells. All eight studies consistently demonstrated that multiple immunizations had no effect on the incidence of Type 1 diabetes, leading the committee to reject the notion that multiple vaccinations cause an increased risk of the disease.

Likewise, the committee said multiple immunizations do not increase the risk of young children developing various infections, ranging from colds and ear infections to pneumonia and meningitis. The committee based its decision on the results of seven studies, which, despite some variations and limitations, consistently showed that multiple vaccinations either had no effect on the risk of infection or provided some degree of protection against infection.

The committee looked at five studies examining multiple vaccinations and their potential to cause allergic diseases, which reflect a hypersensitivity of the immune system to relatively harmless agents in the environment, like pollens, dust mites, insect venom, and specific foods. Some, but not all, of these studies suggested that certain vaccines increase the risk of developing allergic disorders. Methodological weaknesses and inconsistent findings among the studies, however, led the committee to conclude that there is inadequate evidence to either accept or reject a causal relationship between multiple immunizations and increased risk of allergic diseases, particularly asthma.

Although the committee's review of clinical and epidemiological studies found no link between childhood immunizations and immune system dysfunction, its evaluation of basic science research yielded weak evidence of biological mechanisms by which vaccinations might increase the risk of diabetes or allergies. However, there is strong evidence of mechanisms by which vaccinations could increase the risk for infections. While such biological evidence can never prove causality, it can guide further investigation.

Given that about 25 percent of parents in a recent survey agreed with the statement that getting too many vaccines is not good for a baby and can weaken the immune system, the committee recommended that the U.S. Department of Health and Human Services convene an expert panel to examine parents' perceptions of vaccine risks and benefits in order to develop better communication tools for them and their doctors.

This study is the third in a series on vaccine safety sponsored by the Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases. The Institute of Medicine is a private, nonprofit institution that provides health policy advice under a congressional charter granted to the National Academy of Sciences. A committee roster follows.

Michael Kaback, M.D.1Professor of Pediatrics and Reproductive MedicineUniversity of California San Diego

Gerald Medoff, M.D.Professor of Medicine and Microbiology and Immunology, and Senior Adviser to the Chairman of the Internal Medicine DepartmentWashington University School of MedicineSt. Louis

Rebecca Parkin, Ph.D.Associate Research ProfessorDepartment of Occupational and Environmental HealthSchool of Public Health and Health ServicesGeorge Washington University Medical CenterWashington, D.C.

Bennett A. Shaywitz, M.D.1Professor of Pediatrics and Neurology and Chief of Pediatric NeurologyYale University School of Medicine, andCo-DirectorYale Center for the Study of Learning and AttentionNew Haven, Conn.

Christopher Wilson, M.D.Professor and ChairDepartment of Immunology University of Washington Seattle

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Kathleen Stratton, Ph.D.Study Director

1 Member, Institute of Medicine2 Did not attend the meeting on the topic of this report